Scot worried about expense (4)
I believe the answer is:
cost
'expense' is the definition.
(cost is a kind of expense)
'scot worried' is the wordplay.
'worried' indicates an anagram (worry can mean to interfere with or disturb).
'scot' with letters rearranged gives 'COST'.
'about' acts as a link.
(Other definitions for cost that I've seen before include "Charge" , "Come to" , "Be priced at" , "Estimate the expense of doing" , "estimate price" .)